<HTML>
<HEAD>
<!-- Created by texi2html 1.56k from /home/jaffer/scheme/r5rs.txi on 28 March 2001 -->

<TITLE>Revised(5) Scheme - Introduction</TITLE>
</HEAD>
<BODY>
Go to the <A HREF="r5rs_1.html">first</A>, <A HREF="r5rs_1.html">previous</A>, <A HREF="r5rs_3.html">next</A>, <A HREF="r5rs_14.html">last</A> section, <A HREF="r5rs_toc.html">table of contents</A>.
<P><HR><P>


<H1><A NAME="SEC2" HREF="r5rs_toc.html#TOC2">Introduction</A></H1>

<P>
<A NAME="IDX2"></A>


<P>
Programming languages should be designed not by piling feature on top of
feature, but by removing the weaknesses and restrictions that make additional
features appear necessary.  Scheme demonstrates that a very small number
of rules for forming expressions, with no restrictions on how they are
composed, suffice to form a practical and efficient programming language
that is flexible enough to support most of the major programming
paradigms in use today.


<P>
Scheme
was one of the first programming languages to incorporate first class
procedures as in the lambda calculus, thereby proving the usefulness of
static scope rules and block structure in a dynamically typed language.
Scheme was the first major dialect of Lisp to distinguish procedures
from lambda expressions and symbols, to use a single lexical
environment for all variables, and to evaluate the operator position
of a procedure call in the same way as an operand position.  By relying
entirely on procedure calls to express iteration, Scheme emphasized the
fact that tail-recursive procedure calls are essentially goto's that
pass arguments.  Scheme was the first widely used programming language to
embrace first class escape procedures, from which all previously known
sequential control structures can be synthesized.  A subsequent
version of Scheme introduced the concept of exact and inexact numbers,
an extension of Common Lisp's generic arithmetic.
More recently, Scheme became the first programming language to support
hygienic macros, which permit the syntax of a block-structured language
to be extended in a consistent and reliable manner.




<H2><A NAME="SEC3" HREF="r5rs_toc.html#TOC3">Background</A></H2>

<P>
<A NAME="IDX3"></A>


<P>
The first description of Scheme was written in
1975 <A HREF="r5rs_13.html#BIB28">[Scheme75]</A>.  A revised report <A HREF="r5rs_13.html#BIB25">[Scheme78]</A>
 appeared in 1978, which described the evolution
of the language as its MIT implementation was upgraded to support an
innovative compiler <A HREF="r5rs_13.html#BIB26">[Rabbit]</A>.  Three distinct projects began in
1981 and 1982 to use variants of Scheme for courses at MIT, Yale, and
Indiana University <A HREF="r5rs_13.html#BIB21">[Rees82]</A>, <A HREF="r5rs_13.html#BIB17">[MITScheme]</A>, <A HREF="r5rs_13.html#BIB10">[Scheme311]</A>.  An introductory
computer science textbook using Scheme was published in
1984 <A HREF="r5rs_13.html#BIB1">[SICP]</A>.


<P>
As Scheme became more widespread,
local dialects began to diverge until students and researchers
occasionally found it difficult to understand code written at other
sites.
Fifteen representatives of the major implementations of Scheme therefore
met in October 1984 to work toward a better and more widely accepted
standard for Scheme.


<P>
Their report <A HREF="r5rs_13.html#BIB4">[RRRS]</A>
was published at MIT and Indiana University in the summer of 1985.
Further revision took place in the spring of 1986 <A HREF="r5rs_13.html#BIB23">[R3RS]</A>,
and in the spring of 1988 <A HREF="r5rs_13.html#BIB6">[R4RS]</A>.
The present report reflects further revisions agreed upon in a meeting
at Xerox PARC in June 1992.


<P>
We intend this report to belong to the entire Scheme community, and so
we grant permission to copy it in whole or in part without fee.  In
particular, we encourage implementors of Scheme to use this report as
a starting point for manuals and other documentation, modifying it as
necessary.




<H2><A NAME="SEC4" HREF="r5rs_toc.html#TOC4">Acknowledgements</A></H2>

<P>
<A NAME="IDX4"></A>


<P>
We would like to thank the following people for their help: Alan Bawden, Michael
Blair, George Carrette, Andy Cromarty, Pavel Curtis, Jeff Dalton, Olivier Danvy,
Ken Dickey, Bruce Duba, Marc Feeley,
Andy Freeman, Richard Gabriel, Yekta G"ursel, Ken Haase, Robert
Hieb, Paul Hudak, Morry Katz, Chris Lindblad, Mark Meyer, Jim Miller, Jim Philbin,
John Ramsdell, Mike Shaff, Jonathan Shapiro, Julie Sussman,
Perry Wagle, Daniel Weise, Henry Wu, and Ozan Yigit.
We thank Carol Fessenden, Daniel
Friedman, and Christopher Haynes for permission to use text from the Scheme 311
version 4 reference manual.  We thank Texas Instruments, Inc. for permission to
use text from the <EM>TI Scheme Language Reference Manual</EM><A HREF="r5rs_13.html#BIB30">[TImanual85]</A>.
We gladly acknowledge the influence of manuals for MIT Scheme<A HREF="r5rs_13.html#BIB17">[MITScheme]</A>,
T<A HREF="r5rs_13.html#BIB22">[Rees84]</A>, Scheme 84<A HREF="r5rs_13.html#BIB11">[Scheme84]</A>,Common Lisp<A HREF="r5rs_13.html#BIB27">[CLtL]</A>,
and Algol 60<A HREF="r5rs_13.html#BIB18">[Naur63]</A>.


<P>
We also thank Betty Dexter for the extreme effort she put into
setting this report in TeX, and Donald Knuth for designing the program
that caused her troubles.


<P>
The Artificial Intelligence Laboratory of the
Massachusetts Institute of Technology, the Computer Science
Department of Indiana University, the Computer and Information
Sciences Department of the University of Oregon, and the NEC Research
Institute supported the preparation of this report.  Support for the MIT
work was provided in part by
the Advanced Research Projects Agency of the Department of Defense under Office
of Naval Research contract N00014-80-C-0505.  Support for the Indiana
University work was provided by NSF grants NCS 83-04567 and NCS
83-03325.


<P>
   


<P><HR><P>
Go to the <A HREF="r5rs_1.html">first</A>, <A HREF="r5rs_1.html">previous</A>, <A HREF="r5rs_3.html">next</A>, <A HREF="r5rs_14.html">last</A> section, <A HREF="r5rs_toc.html">table of contents</A>.
</BODY>
</HTML>
